ABSTRACT- Relationships among diameter, height, and annual growth were studied in a Stenocereus aragonii (F.A.C. Weber) Buxbaum (Cactaceae) population in Parque Nacional Palo Verde, Costa Rica. Growth occurred in two phases, an initial one of a diameter growth and a later one of height growth. For small plants (<0.5 m height), height and diameter increased together. For larger plants (>0.5 m height), diameter and height were weakly, but significantly, related, indicating that diameter changes little during height growth. The slope of the allometric equation relating diameter and height was much higher than that typical of woody plants, but similar to those of other arborescent, nonwoody plants (palms and other cacti). Since this species has waxy bands indicating annual height growth, it was possible to estimate growth rates. The relative height growth (proportion increase per year) of larger plants was negatively correlated with height; this correlation reduces the likelihood of height transgressing the limit of mechanical stability. Since the study population grew on a ridge where the plants were exposed to strong wind and insolation during the dry season, drought stress or mechanical damage may be important factors that reduce the growth rates of taller plants.